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The recent theory of the interaction of sound with a burning propellant surface is extended to include density fluctuations of the solid propellant. Both compressibility and thermal expansion are treated, but the latter is found to be less important than the former. For reasonable values of the compressibility, it is shown that the acoustic response, Real (μ1/e), of the surface is reduced by as much as 0.1 in a broad range of frequency around several Kc. A simple low‐frequency approximation for the burning surface response is also discussed.

The vibrational relaxation of N2–HI mixtures in the temperature range 1000–2700°K and of N2–DI mixtures in the range 1200–2000°K has been studied behind incident shock waves by time‐resolved measurement of the postshock density gradient using a laser‐beam deflection technique. In both systems the vibrational relaxation of N2 is dominated by vibration–vibration (V–V) energy transfer from the halide gas; contributions due to translation–vibration (T–V) and/or rotation–vibration (R–V) energy transfer are negligible. V–V energy transfer is more efficient in N2–HI than in N2–DI collisions, but the difference is much less than predicted by the SSH theory. Results for the effect of N2 on the relaxation of HI and DI support previous suggestions that R–V energy transfer is the dominant mechanism for vibrational relaxation of the hydrogen halides.

The vibrational relaxation of HCl and DCl has been studied behind incident shock waves in the temperature range 700°–2100°K. Relaxation was followed by time‐resolved measurement of the postshock density gradient using a laser‐beam‐deflection technique. Hydrogen chloride is found to relax more rapidly than DCl. The relaxation times obtained at temperatures above 1000°K are summarized by the expressions (Pψ)HCl = (4.21 ± 0.14) × 10−7exp[(64.0 ± 5.7) (T−1/3 − 0.090)]atm·sec(1000°–2000°K), and (Pψ)DCl = (7.41 ± 0.09) × 10−7exp[(77.7 ± 2.1) (T−1/3 − 0.090)]atm·sec(1000°–2100°K). The values depart from Landau–Teller behavior at lower temperatures. These results are in serious disagreement with those of Borrell and with predictions of the SSH theory. However, they are in good agreement with the theory of Moore, suggesting that rotation–vibration energy transfer is important in the relaxation of HCl and DCl. Possible effects of strong dipole interactions are also discussed.

The vibrational relaxation of pure Cl2 in the temperature range 400–1400°K, and of binary mixtures of Cl2 with CO, HCl, and DCl in the range 400–1100°K has been studied behind incident shock waves by time‐resolved measurement of the postshock density gradient using a laser‐beam deflection technique. Results obtained for pure Cl2 are more precise than those previously available at these temperatures, and are in excellent agreement with lower‐temperature ultrasonic data. The effect of CO relative to Cl2 is found to be much less than indicated by previous data, and is attributed solely to the lower Cl2–CO reduced collision mass. The effects of HCl and DCl are large, particularly at low temperatures, e.g., HCl is ≈100 times more effective than Cl2 at 400°K. HCl is ≈2–4 times more effective than DCl, depending on the temperature. The relative efficiencies are interpreted as a strong indication of rotational effects.

The vibrational relaxation of nitrogen in the presence of oxygen atoms generated by the decomposition of ozone has been studied behind incident shock waves in the temperature range 3000°–4500°K. Relaxation of the nitrogen was followed by measurement of the postshock density gradient using a laser‐beam deflection technique. Analysis of the data to yield PτN2–O, the relaxation time for nitrogen dilute in 1 atm of oxygen atoms, requires consideration of the simultaneous effect of molecular oxygen produced by the ozone decomposition The values obtained for PτN2–O are subject to some uncertainty, but clearly lie below those for pure nitrogen by nearly two orders of magnitude. The results are interpreted as evidence of a chemical effect.

The rate of disappearance of OH following [OH]max in shocked H2–O2–Ar mixtures has been measured by a refined ultraviolet line absorption technique. Thirty‐one experiments have been done with mixtures of 4% H2, 1% O2, 95% Ar; 2% H2, 0.5% O2, 97.5% Ar; and 8% H2, 1% O2, 91% Ar at initial pressures between 50 and 200 mm Hg. The approximate rate equation found to describe the OH disappearance is −d[OH]/dt=kapparent[OH]2[M], where [M] is total gas concentration. Assuming that the equilibrium relationship α=[OH]/[H]=K[H2O]/[H2] is maintained, and that the recombination reactions are: H+H+M→ lim k1H2+M, and H+OH+M→ lim k2H2O+M,kapparent may be interpreted as (A/α) (k1+αk2) where A is a factor near unity which incorporates the definitions of the k's as volumetric rate coefficients, the small variation of α and density during the reaction, and the participation of O and O2. (k1+αk2) increased linearly with α between α=0.01 and α=0.1, yielding k1=6±1×108 liter2 mole—2·sec—1 and k2/k1≈10±5. No dependence on tempera...

The thermal dissociation rate of NF3 in mixtures of 5% and 10% NF3 in Ar has been measured behind incident shock waves over the temperature range 1330–2000 K. Dissociation rates were determined from postshock density gradients measured by laser beam deflection. The second order rate coefficient determined for NF3–Ar collisions is kd=2.31×1015 exp(−20500/T) cm3 mole sec.